The present invention generally relates to an apparatus and a method for removing coating layers from alignment marks on a wafer and more particularly, relates to an apparatus and a method for removing coating layers from the alignment marks by mounting two additional solvent dispensing nozzles in an edge bevel removal (EBR) chamber for spraying a solvent on the coating layers while the wafer is held in a stationary position.
Deposition and patterning are two of the basic steps performed in semiconductor processing. Patterning is also referred to as photolithography, masking, oxide or metal removal, and microlithography. Patterning enables the selective removal of material deposited on a semiconductor substrate, or wafer, as a result of deposition. For example, as shown in FIG. 1A, a layer 104 has been deposited on a substrate 102. After the photolithography process is performed, as shown in FIG. 1B, some parts of the layer 104 have been selectively removed, such that gaps 106a and 106b are present within the layer 104. A photomask, or pattern, is used (not shown in FIG. 1B) so that only the material from the gaps 106a and 106b are removed, and not the other portions of the layer 104. The process of adding layers and removing selective parts of them, in conjunction with other processes, permits the fabrication of semiconductor devices.
Alignment is critical in photolithography and deposition, as well as in other semiconductor processes. If layers are not deposited properly, or if they are not selectively removed properly, the resulting semiconductor devices may not function, relegating them to scrap, which can be costly. Therefore, alignment marks are placed on the semiconductor wafer for the proper positioning during the deposition and photolithography processes. This is shown in FIG. 2, where the semiconductor wafer 202 has alignment marks, such as the alignment square 204, thereon. When the photomask 206 is positioned over the wafer 202, its own alignment marks, such as the alignment square 208, is aligned with the alignment marks of the wafer 202. For example, the alignment square 208 of the photomask 206 is aligned so that the alignment square 204 of the wafer 202 is centered therein.
Alignment is especially critical where more a number of metal or other layers have already been deposited on the wafer. Subsequent deposition of silicon dioxide or other layers in such instances usually requires that the alignment marks on the wafer be exposed for proper overlay of the silicon dioxide or other layers. While a mask may prevent the layers themselves from obfuscating the alignment marks, the photoresist used to pattern or perform other processing of these layers cannot be masked, and covers or at least blurs the alignment marks. Without clear exposure of the alignment marks, however, overlay misalignment can result. Overlay misalignment is also referred to as overlay registration error. Misalignment is a serious problem, and can result in significant semiconductor wafer scrap. Wafer scrap can sometimes be reused, but often is discarded, resulting in added costs incurred by the semiconductor foundry.
In the recent development of semiconductor fabrication technologies, copper has been widely used in devices of 0.18 xcexcm or smaller as vias or interconnects. A widely used technique for depositing copper on a semiconductor wafer is the electrochemical plating method. However, when copper is deposited onto a wafer surface by the electrochemical plating method, alignment marks on the wafer are also covered with a layer of copper and a layer of TaN which is used as a diffusion barrier for copper. If the Cu/TaN layers over the alignment marks are not completely removed in a later process, alignment failure occurs in a future photolithographic step.
Presently, a process of edge bevel removal (EBR) is used to remove a circular band of Cu/TaN at the wafer edge. This is shown in FIG. 3. Wafer 302, which has alignment marks 304 and 306 formed on an active surface 308, is cleaned by using a cleaning solution such that a circular band 310 of Cu/TaN at the wafer edge is removed. Although the Cu/TaN layers over the alignment marks 304,306 is removed, the cleaning procedure inevitably results in die loss along the circular band 310. For instance, as shown in FIG. 3, the IC dies 312xcx9c330 are all lost due to the EBR process.
A typical electrochemical plating (ECP) apparatus 400 which includes an edge bevel removal (EBR) chamber 402 is shown in FIG. 4. The EBR chamber is arranged in a stacked bevel clean and spin rinse/dry chambers for convenient wafer transfer and space saving. The electrochemical plating apparatus 400 further includes two loadlock chambers 404,406 for loading/unloading unprocessed/processed wafers into and out of the apparatus 400. Wafer transfer stations 408 and 410 are used to transfer wafers between the loadlock chambers 404,406, the EBR chambers 402 and the anneal chambers 412 and 414. Within the apparatus 400, is a dual-blade robot 416 used to transfer wafers between the process stations 418, 420 each having a dual cell arrangement for conducting the electro-chemical plating operation. As previously shown in FIG. 3, while the EBR chamber 402 is able to remove coating layers from the top of alignment marks 304,306, the excessive number of IC dies that are lost due to the edge bevel removal process cannot be tolerated if a high fabrication yield is desired.
It is therefore an object of the present invention to provide an apparatus for removing coating layers from alignment marks that does not have the drawbacks or the shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for removing coating layers from alignment marks on a wafer in an edge bevel removal chamber of a plating apparatus.
It is a further object of the present invention to provide an apparatus for removing coating layers from the top of alignment marks by installing at least two solvent spray nozzles in an edge bevel removal chamber for removing the coating layers while the wafer is held in a stationary position.
It is another further object of the present invention to provide an apparatus for removing coating layers from the top of alignment marks on a wafer by first spraying a solvent on the alignment marks while the wafer is stationary and then spraying solvent on the edge bevel while the wafer is rotated.
It is still another object of the present invention to provide an apparatus for removing coating layers from the top of alignment marks by spraying a H2SO4-containing solvent on the coating layers while the wafer is held in a stationary position.
It is yet another object of the present invention to provide a method for removing coating layers from the top of alignment marks on a wafer in a wafer edge cleaning chamber of an electrochemical plating apparatus.
In accordance with the present invention, an apparatus and a method for removing coating layers from the top of alignment marks in a wafer edge bevel removal chamber are disclosed.
In a preferred embodiment, a wafer edge bevel removal chamber for cleaning wafer edge alignment marks is provided which includes a cleaning chamber that has a cavity therein and a lid member suspended in the cavity; a wafer chuck rotatably mounted in the lid member for holding a wafer with an active surface of the wafer and at least two alignment marks on the active surface in a faced-down position; and at least two solvent dispensing arms mounted in an outer peripheral area of the lid member adjacent to the chuck for dispensing a flow of solvent upwardly toward the active surface of the wafer when the wafer is held in a stationary position, each of the at least two solvent dispensing arms are positioned corresponding to a position of one of the alignment marks.
In the wafer edge bevel removal chamber for cleaning wafer edge alignment marks, the EBR chamber is part of an electro-chemical plating (ECP) apparatus. The chamber may further include at least one solvent dispensing arm for dispensing a flow of solvent onto the active surface of the wafer for removing an edge bevel area when the wafer is rotated by the wafer chuck. The flow of solvent may be an H2SO4-containing solvent. The flow of solvent may include H2SO4, H2O2 and deionized water. The ECP apparatus may further include a wafer orientor for mounting the wafer on the wafer chuck in such a way that the alignment marks are at predetermined positions. The alignment marks may be coated with a copper layer. The at least two solvent dispensing arms are mounted such that solvent dispensing nozzles spray a solvent onto the alignment marks at a distance of about 6 mm from a wafer edge.
The present invention is further direct to a method for removing a coating layer on an alignment mark on a wafer in a wafer edge cleaning chamber which can be carried out by the operating steps of first providing a cleaning chamber that has a cavity therein and a lid member suspended in the cavity; providing a wafer chuck rotatably mounted in the lid member for holding a wafer with an active surface of the wafer and at least two alignment marks on the active surface in a faced-down position; mounting at least two solvent dispensing arms in an outer peripheral area of the lid member immediately adjacent to the chuck; and dispensing a flow of solvent upwardly toward the active surface of the wafer when the wafer is held in a stationary position, each of the at least two solvent dispensing arms is positioned corresponding to a position of one of the alignment marks.
The method for removing a coating layer on an alignment mark on a wafer may further include the step of dispensing a flow of solvent onto the active surface of the wafer and removing an edge bevel area when the wafer is rotated by the wafer chuck after the alignment mark cleaning step. The method may further include the step of dispensing a H2SO4-containing solvent onto the alignment marks, or the step of dispensing a solvent including H2SO4, H2O2 and deionized water onto the alignment marks. The method may further include the step of pre-orienting the wafer in an orientation chamber prior to the step of removing coating layers, or the step of removing a copper layer from the alignment marks, or the step of removing copper/tantalum nitride layers from the alignment marks.